Chromatography Forum

For an analytical method we have set a criteria of an RSD of 2.0% or less for the repeatability of six standard areas at the start of the run and a limit of 2.5% or less for all of the run.

We typically see values of 0.5% and 1.0% for the first six and all standards respectively and over 50+ runs have not exceed 1.0 and 2.0%, should I reduce the criteria in respect of what we areactually obtaining or will I be creating a rod for my own back and increasing the risk of failure?

Thanks
Chris

What we do -

For dilute samples (dissolution samples of things with weak chromophores, low area counts) - we go with a 5% limit on standard RSD for initial standards and we stick with it for the run. If RSD strays above 5%, we'll try nested bracketing and reinject any sample sets not bounded by standards that meet the 5% criterion.

For more concentrated samples, it is as above but with a 2% criterion.

Also, do you think a target retention time of 9.0 to 12.0 minutes is too wide?

We do not set windows in our methods. We specify that the chromatograms look approximately like the example(s) provided. We also typically specify a minimum resolution between whatever the critical peak pair is for a given method.